package binary_tree;

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

public class LevelOrderBottom {
    public List<List<Integer>> levelOrderBottom(TreeNode root) {
        List<List<Integer>> list = new ArrayList<>();
        if(root == null){
            return list;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);
        while(!queue.isEmpty()){
            int size = queue.size();
            List<Integer> list1 = new ArrayList<>();
            while(size != 0){
                TreeNode cur = queue.poll();
                list1.add(cur.val);
                if(cur.left != null){
                    queue.offer(cur.left);
                }
                if(cur.right != null){
                    queue.offer(cur.right);
                }
                size--;
            }
            list.add(0,list1);
        }
        return list;
    }
}
